An important process for the conversion of the higher boiling fractions of crude oil, such as vacuum gas oil (VGO) and reduced crudes, to form gasoline and heating fuels is by fluid catalytic cracking. Fluid catalytic cracking (FCC) is commonly used to process VGO feedstocks and may be used for residual oils or reduced crudes. The residual oil feedstock is contacted in such an FCC operation with a fluidizable catalyst at elevated temperatures for short vapor contact times at low pressures; separation of catalyst and gaseous products is affected with stripping of the separated and coked catalyst followed by catalyst regeneration and recycle of the regenerated catalyst to hydrocarbon conversion to repeat the process.
One of the major problem areas in heavy oil, residual oil cracking operations is the deposition of the contaminant metals present in the (VGO) vacuum gas oil and reduced crudes on the catalyst during the fluid cracking operations. These contaminant metals include Ni--V--Fe--Cu. As the concentration of these metals increase on the catalyst, the rate of undesirable side reactions generated by these contaminant metals increases. These undesirable reactions include dehydrogenation, coking, and methyl group removal which leads to increased feedstock conversion accompanied by lower selectivity to desired products and increased coke production. The dehydrogenation reaction leads to increased hydrogen production, methyl clipping to increased methane production and the production of these light gases give decreased gasoline production (lower selectivity) and increase substantially the demand for compressor capacity to handle these light gases.
The published art teaches many techniques to handle undesirable reactions exhibited by encountered contaminant metals above identified. These techniques include contaminant metal removal and passivation. Examples of techniques for metal removal are taught and claimed in U.S. Pat. Nos. 3,122,511; 3,122,512; 3,148,155; 3,192,151 and 4,014,815. Examples of techniques for metal passivation are taught and claimed in U.S. Pat. Nos. 3,711,422 (antimony); 3,977,963 (manganese); 4,101,417 (tin); 4,192,770 (boron). Other techniques for passivating or reducing the undesirable reactions of these contaminant metals include the precoking with methane as described in U.S. Pat. No. 3,120,484; sulfiding of the metals to form the metal sulfide as described in U.S. Pat. No. 3,838,038 and copending application U.S. Ser. No. 099,050; now abandoned; the reduction of the metal oxides with hydrogen and carbon monoxide in U.S. Pat. Nos. 4,268,416; 4,280,895 and 4,280,896.